In the process industry, one of the biggest sources of failures and shutdown for process plants is in pressurised piping and vessel systems. In the prior art, systems are known which monitor and assess plants in order to be able to predict a failure. According to the prior art, the wall thickness of structures, such as piping, is simply monitored in order to perform simple calculations and to predict a trend, for instance in the wear and/or the corrosion of such a structure. Alternatively, machinery-based corrosion and vibration monitoring systems are used. These systems are grossly inaccurate as over 85% of failures occur at non-straight pipe areas, due to structural loadings, corrosion/erosion, fatigue, pulsation or vibration (“Hydrocarbon” magazine). The monitoring and assessment technologies according to the prior art are based on “risk analysis”. These systems use probability to estimate failure, and in doing so predict suitable inspection intervals. An important disadvantage of such an approach is that these systems do not use real-time measurements in order to calculate real-time load and load changing mechanisms.
A system for monitoring a pipe segment for instance is known from the European Patent Application EP 0358994. The method according to EP 0358994 is adapted to measure a corrosion/erosion trend. The system is confined to the change in the main pipe wall thickness to predict the future thickness of the pipe wall. According to this document the emphasis is on measuring the corrosion/erosion rate and using statistical techniques to predict future rates and trends. The estimated stress in a pipe wall is calculated using the following equation:
  Stress  =                    pressure        ×        radius            thickness        ×    estimated    ⁢                  ⁢    factor  
This equation only calculates pressure loading in straight pipes. No other loadings are considered. As the thickness decreases there is a danger of pipewall rupture. Therefore the information is used in order to predict the maximum time interval before the next inpection of the pipe welds. The information collected according to EP0358994, in practice, is not very helpful, as very few plant failures are caused by main pipewall rupture. This means that the information collected by means of EP0358994 has only limited value.
U.S. Pat. No. 4,852,397 discloses a procedure for measuring material properties of a structure. The method is used to test the material properties of a failed structure. The results are used to determine if the remaining structure is safe to dismantle or even partially remain in service. This system does not indicate in any way, how to measure the loads or geometry of any system, let alone how to further predict the integrity of such a structure. This method can only be used as a destructive method of determining material behaviour such as a Stress-Strain Curve and Fracture Toughness.
US-2001-040997 discloses a method for tracking moving objects such as skin. It is designed for Motion Tracking and bears no relevance to Integrity Monitoring. The fact that it uses a Finite Element Analysis technique is irrelevant because this method is used for many applications. The iterative approach used according to D2 is to re-mesh the Finite Element Model to simulate the skin motion and is an iterative approach so as to allow the mesh to move, thus tracking the motion. It is not modelling a whole structure. It is not modelling any loadings that would be relevant, nor does it measure systems characteristics and use these to predict its Integrity. It simply teaches that a localised Finite Element Grid can be used to track motion.
Additionally, according to the prior art it is known to use acoustic pulsation, vibration and condition monitoring in order to monitor and assess the integrity of a structure. The disadvantage of those techniques is the fact that those techniques are both specialist tasks and extremely expensive. Because of the high costs involved with those techniques normally these techniques are only undertaken if failure is expected or has occurred.